1. Technical Field
The present disclosure generally relates to a wireless service handover scheme, a relay station using the same and a donor eNodeB using the same.
2. Related Art
Recently, as many countries continue to build their high speed rail systems, mobile relay techniques have been considered for the IMT-advanced system in order to support wireless communication services within a high speed rail system in which mobile relays situated on a train carriage could relay network services from nearby base stations to users. The mobile relay which functions as a hub or a repeater may then provide the network coverage of a base station to users in a train through a cable or through a wireless connection.
Such mobile delay technique has been discussed in a LTE-A standard working group in order to support the high speed rail scenario. A typical scenario may include mobile relays equipped in every carriage of a train, and users in a carriage may connect to a nearest mobile relay which subsequently plays the role of an eNB for users. A mobile relay may redirect received data from users to a donor eNB (DeNB) deployed along a train route. On the other hand, a mobile relay may also distribute data from a communication network to users.
As passengers travel through long distances between countries in Europe or among provinces in China, accessibility to a communication network may be desirable for a passenger taking the high speed rail since it would allow the user to remain productive while waiting for the destination to arrive. A users may enjoy activities such as Internet surfing, watching on-line videos, and processing e-mails in the high speed rail, and so forth.
However, for a typical high speed rail system, a mobile relay situated on a fast moving train would speed through an area of coverage provided by a DeNB in a very short period of time. Assuming that a train having the speed as high as 350 kilometers per hour travels through a 2 kilometer coverage area of a serving DeNB, the train would only be in the 2 km area for merely 20.6 seconds. In other words, the mobile relay is only served by its serving DeNB for 20.6 seconds. This means that as the train traverses along the train route, it would suffer from frequent handovers between DeNBs, and also a DeNB would have very little time to make handover decisions.
Therefore, it is important to design a very quick and still yet reliable handover scheme so as to allow users to communication services in a high speed rail.